METHODS OF STIMULATION 27 



means of which the rays can be focused upon any point that 

 is desired. 



Stimulation by Constant Current 



I have found that Mimosa and other sensitive plants show 

 certain very remarkable excitatory effects under the action 

 of a constant current. The characteristic feature of these 

 is that excitation is not induced during the passage of the 

 current but only at its initiation or cessation. The excita- 

 tory effect in this case is further conditioned by the point 



Fig. 8. — Responses to stimulation by constant 

 electric current. 



of entry, or anode, and that of exit, or kathode. The 

 specific characteristics of this mode of stimulation will be 

 found fully described in the chapter on the Polar Effects 

 of Currents in Excitation. It need only be mentioned here 

 that, in the matter of all these peculiar effects, the plant 

 tissue behaves in a manner exactly similar to the animal 

 tissue. A series of records obtained from Mimosa by the 

 stimulus of a constant current are shown in fig. 8. 



Stimulation by Condenser Discharge 



Another practical method of stimulation is that of 

 condenser discharge. The condenser consists essentially 

 of two conducting-plates — which may be two sheets of 



